Transmission apparatus

ABSTRACT

A wireless communication system includes an amplitude limiting section that limits an amplitude of a sequence of signals input for transmission and a nonlinear distortion compensating section compensates nonlinear distortion of the sequence of signals output from the amplitude limiting section. A digital wireless communication method is also provided.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is a Continuation of U.S. application Ser. No.09/101,443, filed Jul. 15, 1998, which was the National Stage ofInternational Application No. PCT/JP97/04132, filed Nov. 13, 1997, thecontents of which are herein incorporated by reference in theirentireties. The International Application was not published under PCTArticle 21(2) in English.

TECHNICAL FIELD

[0002] The present invention relates to a nonlinear distortioncompensating technique in a transmission apparatus for digital radiocommunications.

BACKGROUND ART

[0003] In recent years, a mobile communication system using a digitalmodulation method has vigorously been researched and developed. If ahigh efficiency amplifier is employed in the transmission system inorder to attempt to save power at a radio transceiver, nonlineardistortions frequently result therefrom. As a means, there is a methodfor compensating nonlinear distortions of amplitude and phase withreference to a distortion compensating table, by using an amplitudevalue of transmission base band signals.

[0004] A description is given of a conventional transmission apparatuswhich compensates nonlinear distortions by using such a method.

[0005]FIG. 10 is a main block diagram of a conventional transmissionapparatus. In FIG. 10, amplitude calculating section 1001 calculatesamplitude information 1010 of transmission signals 1009 (transmissiondigital quadrature base band of I and Q channels), and compensationtable 1002 outputs distortion compensating coefficient 1011. Thedistortion compensating section 1003 outputs a distortion compensatingsignal 1012 according to the transmission signal 1009 and distortioncompensating coefficient 1011. The outputted distortion compensationsignal 1012 is quadrature-modulated by quadrature modulating section1004, and the modulated signal 1013 is amplified by amplifier 1005,wherein amplified RF signal 1014 is outputted.

[0006] Furthermore, demodulating section 1007 demodulates feedback RFsignal 1016 fed back from coupler 1006 to feedback base band signal1017, and estimating section 1008 updates the distortion compensationcoefficient of compensation table 1002 on the basis of a distortioncompensation coefficient 1018, transmission signal 1009 and feedbackbase band signal 1017. Through the abovementioned actions, amplified RFsignal 1015 for which nonlinear distortion compensation is carried outis outputted from the coupler 1006.

[0007] In addition thereto, as a method to compensate nonlineardistortions in the transmission system, there is a method having adigital filter to which a ROM (Read-only-memory) is attached, whereincompensation is carried out by applying in advance distortions tocompensate nonlinear distortions generated in an amplifier by thedigital filter.

[0008] The main block diagram of a conventional transmission apparatusin which this method is employed is shown in FIG. 11. Hereinafter, adescription is given to this apparatus.

[0009] In FIG. 11, digital filter 1102 in which digital signals 1101 isinputted gives to the digital signal 1101 distortions to compensatenonlinear distortion components generated in radio frequency poweramplifier 1105, by using distortion information stored in a ROM inadvance.

[0010] The digital signal 1101 to which distortion to be compensated isgiven is digital-analog converted and modulated by quadrature modulatingsection 1103 and inputted into the radio frequency power amplifier 1105via transmission section 1104. In the radio frequency power amplifier1105, since distortion of the inputted digital signal are compensated inadvance, distortions generated at the radio frequency power amplifier1105 are cancelled by those for compensation.

[0011] Furthermore, instead of ROM, there is still another method tocompensate nonlinear distortions, in which a RAM (Random Access Memory)having compensation coefficients stored therein in order to compensatenonlinear distortion components is used, by varying the compensationcoefficients of the RAM in compliance with amplitudes of digitalsignals.

[0012] Furthermore, Unexamined Japanese Patent Publication No. 290321 of1992 discloses a method for controlling actions of a digital filter byfeeding outputs of a radio frequency power amplifier back to the digitalfilter.

[0013] However, in the conventional example shown in FIG. 10, it isnecessary that signals having the maximum amplitude is suppressed lessthan the maximum output of amplifier 1005, and this results in alowering of efficiency in the amplifier 1005.

[0014] In the conventional example shown in FIG. 11, since it isnecessary to provide a memory table such as a ROM or RAM in whichcompensation coefficients are stored to compensate nonlinear distortioncomponents, and this results in an increase of the scale of transmissioncircuits themselves.

DISCLOSURE OF INVENTION

[0015] It is therefore an object of this invention to provide atransmission apparatus capable of easily controlling leak power andeasily improving the efficiency of power amplification and cable ofcompensating nonlinear distortions generated in a transmission systemamplifier without any use of a memory table such as a ROM or RAM.

[0016] The first aspect of the invention resides in a transmissionapparatus having a nonlinear distortion compensating circuit, whichincludes an amplitude limiting function for transmission quadrature baseband signals by adding an amplitude calculating section, an amplitudelimiting table and an amplitude limiting section thereto. Thereby, it ispossible to easily improve the efficiency of amplification section withdistortions of the entire system limited.

[0017] The second aspect of the invention is such that nonlineardistortion compensation is carried out on the basis of nonlineardistortion compensation coefficients calculated by an approximationequation in a compensation coefficient calculating section. Thereby, itis possible to compensate nonlinear distortions generated by amplifierin the transmission system without any use of a memory table such as aROM or RAM, and it is possible to make a nonlinear distortioncompensating section small-sized.

[0018] Furthermore, this invention is constructed so that it is providedwith a first amplitude calculating section for calculating the firstamplitude value of transmission quadrature base band signals; anamplitude limiting table for storing amplitude limiting informationcorresponding to the first amplitude value; a first amplitude limitingsection for limiting the amplitude of the transmission quadrature baseband signals by using the amplitude limiting information; a quadraturemodulating section for outputting RF signals by quadrature-modulatingthe transmission quadrature base band signals, the amplitude of which islimited; and an amplification section for amplifying the RF signals.

[0019] With this construction, it is possible to improve the efficiencyof an amplifying section with distortion components limited, byexecuting distortion compensation of an amplifier with respect tolimited signals, the maximum amplitude of which is distorted by thetransmission quadrature base band signals.

[0020] Furthermore, the invention is constructed so that it is providedwith a first amplitude calculating section for calculating the firstamplitude value from transmission quadrature base band signals; alimiting coefficient calculating section for calculating an amplitudelimiting coefficient corresponding to the first amplitude value; asecond amplitude limiting section for limiting the amplitude of thetransmission quadrature base band signal by using the amplitude limitingcoefficient; a quadrature modulating section for quadrature-modulatingthe transmission quadrature base band signals to output RF signals, theamplitude of which is limited; and an amplification section foramplifying the RF signals.

[0021] With this construction, the amplitude limiting coefficient iscalculated on the basis of amplitude information of the transmissionquadrature base band signals, whereby it is possible to improve theefficiency of amplifier by limiting the amplitude of transmissionsignals in compliance with the amplitude limiting coefficient with thedistortion components limited, without adding any memory thereto.

[0022] Furthermore, this invention is constructed so that it is providedwith a power calculating section for calculating a power value oftransmission quadrature base band signals; a compensation coefficientcalculating section for calculating a nonlinear distortion compensationcoefficient according to approximation equation set in advance using thepower value; a distortion compensating section for carrying outnonlinear distortion compensation of the transmission quadrature baseband signals by using the nonlinear distortion compensation coefficient;a quadrature modulating section for quadrature-modulating transmissionquadrature base band signals, the distortion of which is compensated;and an amplifier for amplifying the quadrature modulation signal.

[0023] With this construction, with only slight memory capacity, it ispossible to compensate nonlinear distortion which is generated at anamplifier of transmission system.

[0024] Furthermore, the invention is constructed so that it is providedwith a power calculating section for calculating a power value oftransmission quadrature base band signals; a compensation coefficientcalculating section for calculating an amplitude distortion compensationcoefficient by an approximation equation set in advance by using thepower value; a quadrature modulating section for quadrature-modulatingthe transmission quadrature base band signals; and an amplitudedistortion compensating section for compensating amplitude distortionsof quadrature modulation signals using the amplitude distortioncompensation coefficient.

[0025] With this construction, it is possible to compensate amplitudedistortions, which is generated at an amplifier of transmission system,with simple calculations and slight memory capacity.

[0026] Furthermore, the invention is constructed so that it is providedwith a power calculating section for calculating a power value oftransmission quadrature base band signals; a compensation coefficientcalculating section for calculating an amplitude distortion compensationcoefficient by an approximation equation set in advance by using thepower value; a quadrature modulating section for quadrature-modulatingthe transmission quadrature base band signals; an amplitude distortioncompensating section for compensating amplitude distortions ofquadrature modulation signals by using the amplitude distortioncompensating coefficient; an amplifier for amplifying modulationsignals; a distributor for distributing output of the amplifier; aquadrature demodulator for carrying out quadrature demodulate with oneof the outputs of the distributor inputted; and a coefficient updatingsection which calculates an error by comparing quadrature demodulatesignals with the power value and updates the value of coefficients ofthe approximation equation on the basis of the error.

[0027] With this construction, it is possible to very accuratelycompensate amplitude distortions by lowering the error of amplitudedistortion compensation data calculated by an approximation equationthrough a feedback loop.

BRIEF DESCRIPTION OF DRAWINGS

[0028]FIG. 1 is a main block diagram of a transmission apparatusaccording to a first embodiment of the invention,

[0029]FIG. 2 is a main block diagram of a transmission apparatusaccording to a second embodiment of the invention,

[0030]FIG. 3 is a main block diagram of a transmission apparatusaccording to a third embodiment of the invention,

[0031]FIG. 4 is a main block diagram of a transmission apparatusaccording to a fourth embodiment of the invention,

[0032]FIG. 5 is a main block diagram of a transmission apparatusaccording to a fifth embodiment of the invention,

[0033]FIG. 6 is a main block diagram of a transmission apparatusaccording to a sixth embodiment of the invention,

[0034]FIG. 7 is a main block diagram of a transmission apparatusaccording to a seventh embodiment of the invention,

[0035]FIG. 8 is a main block diagram of a transmission apparatusaccording to a eighth embodiment of the invention,

[0036]FIG. 9 is a main block diagram of a transmission apparatusaccording to a ninth embodiment of the invention,

[0037]FIG. 10 is a main block diagram of a conventional transmissionapparatus, and

[0038]FIG. 11 is a main block diagram of another conventional apparatusother than the above apparatus.

BEST MODE FOR CARRYING OUT THE INVENTION

[0039] Hereinafter, a detailed description is given of embodiments of atransmission apparatus according to the invention.

[0040] (Embodiment 1)

[0041]FIG. 1 is a main block diagram of a transmission apparatusaccording to a first embodiment of the invention.

[0042] A transmission apparatus illustrated in FIG. 1 comprises firstamplitude calculating section 101, amplitude limiting table 102,amplitude limiting section 103, nonlinear distortion compensatingsection 104, quadrature modulating section 108, amplification section109, etc.

[0043] Nonlinear distortion compensating section 104 has secondamplitude calculating section 105, compensating table 106 using a RAM,distortion compensating section 107, coupler 110, demodulating section111, and estimating section 112.

[0044] Furthermore, in FIG. 1, reference number 113 indicate atransmission signal (Transmission digital quadrature base band signal inI and Q channel), reference number 114 indicate amplitude information ofthe transmission signal, reference number 115 indicate an amplitudelimiting coefficient, reference number 116 indicate an amplitudelimiting signal, reference number 117 indicate limiting amplitudeinformation, reference number 118 indicate a distortion compensationcoefficient, reference number 119 indicate a distortion compensationsignal, reference number 120 indicate an RF signal, reference number 121indicate an amplitude RF signal, reference number 122 indicate an outputsignal, reference number 123 indicate a feedback RF signal, referencenumber 124 indicate a feedback base band signal, and reference number125 indicate a coefficient updating signal.

[0045] A description is given of the actions of a transmission apparatusconstructed as described above.

[0046] The first amplitude calculating section 101 calculates amplitudeinformation 114 on the basis of transmission signal 113 and outputs it.In amplitude limiting table 102, proper amplitude limiting informationis stored in advance with respect to a modulation method designed on thebasis of noise margin and leak power value as its entirety, andamplitude limiting coefficient 115 is outputted in response to amplitudeinformation 114.

[0047] Amplitude limiting section 103 limits the amplitude oftransmission signal 113 in accordance with the amplitude limitingcoefficient 115 and outputs an amplitude limiting signal 116 thusobtained. The amplitude limiting executed herein is to limit theprotrudent amplitude in only a slightly short time. Furthermore, it isclear that the leak power of amplitude limiting signal 116 can bedesigned in advance on the basis of a modulation method and amplitudelimiting information.

[0048] Nonlinear distortion compensating section 104 compensatesnonlinear distortions of amplifier 109 almost as in the description withreference to FIG. 10 in the conventional example.

[0049] That is, the second amplitude calculating section 105 calculateslimiting amplitude information 117 from amplitude limiting signal 116and outputs it. Compensation table 106 outputs distortion compensationcoefficient 118 in response to limiting amplitude information 117.Distortion compensating section 107 calculates distortion compensationsignal 119 on the basis of distortion compensation coefficient 118 andamplitude limiting signal 119. Quadrature modulating section 108modulates distortion compensation signals 119 to radio frequency (RF)signals 120 which are signals of carrier band. Amplifier 109 amplifiesthe power of RF signals 120 and outputs amplified RF signals 121.

[0050] Coupler 110 outputs a part of amplified RF signals 121 as afeedback RF signal 123 and outputs the remaining thereof as outputsignals 122. Demodulator 111 demodulates the feedback RF signal 123 to afeedback base band signal 124. The estimating section 112 updates, usingthe amplitude limiting signal 116 as a target value, distortioncompensation coefficients stored in the compensation table 106 by acoefficient updating signal 125 in compliance with a distortioncompensation coefficient 118 read by the coefficient updating signal125, limiting amplitude information 117 and feedback base band signal124.

[0051] As a result, the linearity between amplitude limiting signal 116and feedback base band signal 124 will be retained by a distortioncompensation coefficient stored in compensation table 106.

[0052] The distortion components of the output signal 122 are equalizedto the distortion components of the amplitude limiting signal 116. Asdescribed above, the amplitude limiting signal 116 can be easilydesigned on the basis of modulation method and the amplitude limitinginformation stored in amplitude limiting table 102, wherein it ispossible to control distortion components as the entire system by theamplitude limiting information.

[0053] In a prior nonlinear distortion compensation technique, themaximum amplitude signal is assigned to the maximum output value of anamplifier. However, since signals having the maximum amplitude have avery low ratio of existence, they will not exert any great influence asleak power even though the maximum amplitude signals are slightlydistorted. Therefore, if the amplitude of the maximum amplitude signalsis limited and its average amplitude is relatively raised, it becomespossible to improve the amplification efficiency of an amplifier.

[0054] Thus, according to the first embodiment, since the amplitude ofsignals having a great amplitude is limited before carrying outnonlinear distortion compensation, the maximum amplitude value islowered, wherein the amplifier 121 has an allowance to improve the meanpower.

[0055] On the other hand, distortion components, the amplitude of whichis limited, can be designed in advance on the basis of its modulationsystem and limiting properties, the leak power resulting from thenonlinearity outside the signal band can be suppressed less than theprescribed level, wherein the area of nonlinearity of the amplifier 121is used to cause the efficiency of power amplification to be improved.

[0056] Thus, since it is possible to easily control the distortioncomponents, it is possible to construct a more efficient transmissionapparatus than that according to the prior nonlinear distortioncompensation technique.

[0057] Generally, suppression of signals having a great amplitude iseffective in improving the efficiency. However, it is also possible tosecure the same effect by elongating signals having a small amplitude.Furthermore, by making the amplitude width narrow by a combination ofthe former and the latter, the efficiency can be further improved.

[0058] (Embodiment 2)

[0059]FIG. 2 is a main block diagram of a transmission apparatusaccording to a second embodiment of the invention. However, parts in thesecond embodiment illustrated in this drawing, which correspond to thoseof the first embodiment illustrated in FIG. 1 are given the samereference numbers, and the description thereof is omitted.

[0060] A transmission apparatus shown in FIG. 2 is different from thatshown in FIG. 1 in that, as shown at the nonlinear distortioncompensating section 201 of FIG. 2, the second amplitude calculatingsection 105 of the nonlinear distortion compensating section 104 shownin FIG. 1 is omitted, and amplitude information 114 of the transmissionsignals outputted from the amplitude calculating section 101 isoutputted to the compensation table 106 and estimating section 112.

[0061] In such a construction, amplitude information 114 calculated bythe first amplitude calculating section 101 is outputted to thecompensation table 106 and estimating section 112, and the compensationtable 104 outputs distortion compensation coefficients 118 in compliancewith the amplitude information 114.

[0062] Furthermore, using the amplitude limiting signal 116 as a targetvalue, the estimating section 112 updates the distortion compensationcoefficients stored in the compensation table 106 by a coefficientupdating signal 125 in compliance with distortion compensationcoefficients read from the compensation table 106 by the coefficientupdating signal 125, amplitude information 114, and feedback base bandsignal 124. The other actions are the same as those described in thefirst embodiment.

[0063] Thus, according to the second embodiment, since the nonlineardistortion compensating section 201 is constructed with the amplitudecalculating section omitted in addition to securing the same effects asthose of the first embodiment, the configuration thereof can be furthersimplified than the first embodiment. The entire size thereof can bereduced.

[0064] (Embodiment 3)

[0065]FIG. 3 is a main block diagram of a transmission apparatusaccording to a third embodiment of the invention. However, parts in thethird embodiment illustrated in this drawing, which correspond to thoseof the first embodiment illustrated in FIG. 1 are given the samereference numbers, and the description thereof is omitted.

[0066] A transmission apparatus illustrated in FIG. 4 is different fromthat shown in FIG. 1 in that a limiting coefficient calculating section301 shown in FIG. 2 is provided instead of the amplitude limiting table102 shown in FIG. 1 and the amplitude limiting coefficient 302calculated by the limiting coefficient calculating section 301 isoutputted to the amplitude limiting section 103.

[0067] Furthermore, a limiting coefficient calculating section 301 canbe achieved by a surplus calculation performance of DSP (Digital SignalProcessor) (not illustrated) which is a component of the transmissionapparatus along with the first amplitude calculating section 101 andamplitude limiting section 103.

[0068] In such a construction, in limiting coefficient calculatingsection 301, a proper amplitude limiting coefficient calculation methodis defined in advance with respect to a modulation system which isdesigned on the basis of noise margin and leak power value as the entiresystem, and amplitude limiting coefficients 302 are outputted incompliance with the amplitude information 114. The amplitude limitingsection 103 calculates amplitude limiting signals 116 on the basis ofamplitude limiting coefficient 302 and transmission signal 113.

[0069] The amplitude limiting signal 116 can be easily designed by amodulation system and a calculation method defined by the limitingcoefficient calculating section 301, wherein it is possible to controldistortion components as the entire system by the amplitude limitingcoefficient calculation method. The other actions are the same as thoseof the first embodiment.

[0070] Thus, according to the third embodiment, limiting coefficientcalculation part 301 which already exists as a component of thetransmission apparatus is provided instead of the amplitude limitingtable 102 constructed using memories such as a ROM, etc. in addition tosecuring the same effects as those of the first embodiment. Therefore,it is possible to further simplify the apparatus than the firstembodiment, and the entire system can be small-sized.

[0071] (Embodiment 4)

[0072]FIG. 4 is a main block diagram of a transmission apparatusaccording to a fourth embodiment of the invention. However, parts in thefourth embodiment illustrated in this drawing, which correspond to thoseof the third embodiment illustrated in FIG. 3 are given the samereference numbers, and the description thereof is omitted.

[0073] A transmission apparatus illustrated in FIG. 4 is different fromthat illustrated in FIG. 3 in that, as shown in the nonlinear distortioncompensating section 201 in FIG. 4, the second amplitude calculatingsection 105 of the nonlinear distortion compensating section 104 shownin FIG. 3 is omitted, and amplitude information 114 of transmissionsignals outputted from the amplitude calculation portion 101 isoutputted to the compensation table 106 and estimating section 112.

[0074] In such a construction, the amplitude information 114 calculatedby the amplitude calculating section 101 is outputted to thecompensation table 106 and estimating section 112, wherein thecompensation table 104 outputs distortion compensation coefficients 118in compliance with the amplitude information 114.

[0075] Furthermore, using the amplitude limiting signal 116 as a targetvalue, the estimating section 112 updates distortion compensationcoefficients stored in the compensation table 106 by a coefficientupdating signal 125 in compliance with the distortion compensationcoefficient read from the compensation table 106 by the coefficientupdating signal 125, amplitude information 114 and feedback base bandsignal 124. The other actions thereof are the same as those of the thirdembodiment.

[0076] Thus, according to the fourth embodiment, it is possible toobtain effects similar to those of the third embodiment, and since theamplitude calculating section is omitted from the nonlinear distortioncompensating section 201, it is possible to further simplify theapparatus than the third embodiment, and the entire system can besmall-sized.

[0077] (Embodiment 5)

[0078]FIG. 5 is a main block diagram of a transmission apparatusaccording to a fifth embodiment of the invention. However, parts of thefifth embodiment shown in FIG. 5, which correspond to those of the firstembodiment shown in FIG. 1, are given the same reference numbers, andthe description thereof is omitted.

[0079] In FIG. 5, reference number 501 is a nonlinear distortioncompensating section, reference number 502 is a threshold value storingsection, reference number 503 is an amplitude comparator, referencenumber 504 is a first compensation table, reference number 505 is asecond compensation table, reference number 506 is a coefficientselecting section, reference number 512 is an estimating section,reference number 513 is a writing selecting section, reference number516 is threshold value information, reference number 517 is a result ofamplitude comparison, reference number 518 is a first compensationcoefficient, reference number 519 is a second compensation coefficient,reference number 520 is a distortion compensation coefficient, referencenumber 527 is a coefficient renewing signal, reference number 528 is afirst updating signal, reference number 529 is a second updating signal.

[0080] A description is given of the actions of a transmission apparatusthus constructed. The amplitude calculating section 105 calculates andoutputs amplitude information 117 on the basis of transmission signal116. The threshold value storing section 502 outputs threshold valueinformation 516. The comparator 503 compares amplitude information 117with threshold value information 516, and outputs the result 517 ofamplitude comparison, which shows whether the amplitude is grater orsmaller than the threshold value.

[0081] The first compensation table 504 and the second compensationtable 505 output the first compensation coefficient 518 and the secondcompensation coefficient 519 in compliance with amplitude information117. Coefficient selecting section 506 selects any one of the firstcompensation coefficient 518 and the second compensation coefficient 519on the basis of the result 517 of amplitude comparison and outputsdistortion compensation coefficient 520.

[0082] For example, in a case where the result 517 of amplitudecomparison shows that the amplitude is smaller than the threshold value,the coefficient selecting section 506 selects the first compensationcoefficient 518 and outputs it as distortion compensation coefficient520. If it is shown that the amplitude is greater than the thresholdvalue, the coefficient selecting section 506 selects the secondcompensation coefficient 519 and outputs it as distortion compensationcoefficient 520. The distortion compensating section 107 calculatesdistortion compensation signal 521 on the basis of transmission signal113 and distortion compensation coefficient 520 and outputs it to thequadrature modulating section 108.

[0083] Furthermore, using the transmission signal 514 as the targetvalue, the estimating section 512 renews a coefficient updating signal527 in compliance with the distortion compensation coefficient read ascoefficient updating signal 527 through the write selecting section 513,amplitude information 515, amplitude comparison result 517 and feedbackbase band signal 124 and outputs the first updating signal 528 or thesecond updating signal 529.

[0084] The write section section 513 selects the renewed coefficientupdating signal 527 from the first updating signal 528 and the secondupdating signal 529 on the basis of the amplitude comparison result 517and renews the distortion compensation coefficients of the firstcompensation table 504 or the second compensation table 505. Forexample, in a case where the amplitude comparison result 517 shows thatthe amplitude is smaller than the threshold value, the write selectingsection 513 selects the renewed coefficient updating signal 527 from thefirst updating signal 528 and renews a distortion compensationcoefficient of the first compensation table 504, and in a case where theamplitude comparison result 517 shows that the amplitude is larger thanthe threshold value, the write selecting section 513 selects the renewedcoefficient updating signal 527 from the second updating signal 529, andrenews the distortion compensation coefficient of the secondcompensation table 505.

[0085] Therefore, in a prior nonlinear distortion compensationtechnique, the maximum amplitude signal is assigned to the maximumoutput value of an amplifier. However, since signals having the maximumamplitude have a very low ratio of existence, they will not exert anygreat influence as leak power even though the maximum amplitude signalsare slightly distorted. Therefore, the distortion compensationcoefficient is renewed so as to keep the linearity in the firstcompensation table, and the distortion compensation coefficient isrenewed so as to adjust only the phase in the second compensation table,wherein it is possible to cause signals of a large amplitude to have afeature by which the signals are not greatly distorted since thelinearity is kept at the phase components while the amplitude isproperly limited by a lowering of the gain of the amplifier.

[0086] Furthermore, since the amplitude of the maximum amplitude signalis limited, the mean amplitude is relatively increased, and it ispossible to improve the amplification efficiency of an amplifier.

[0087] Thus, according to the fifth embodiment, since it is possible tocontrol the distortion components with a simple construction, it ispossible to construct a more efficient transmission apparatus than aconventional nonlinear distortion compensation technique.

[0088] (Embodiment 6)

[0089]FIG. 6 is a main block diagram of a transmission apparatusaccording to the sixth embodiment of the invention.

[0090] In FIG. 6, reference number 600 indicate a nonlinear distortioncompensating section, reference number 601 indicate a transmissiondigital quadrature base band signal on I and Q channels, referencenumber 602 indicate a power calculating section, reference number 603indicate an amplitude value calculated in the power calculating section602, reference number 604 indicate a compensation coefficientcalculating section for nonlinear distortion compensation, referencenumber 605 indicate quadrature nonlinear distortion compensation data,reference number 606 indicate a distortion compensating section,reference number 607 indicate a quadrature base band signal for whichnonlinear distortion is compensated, reference number 608 indicate a D/Aconverting section, reference number 609 indicate an analog quadraturebase band signal, reference number 610 indicate a low band pass filterfor limiting the band, reference number 611 indicate a band-limitedanalog quadrature base band signal, reference number 612 indicate aquadrature modulator, reference number 613 indicate a modulation signal,reference number 614 indicate a transmission system amplifier, andreference number 615 indicate an amplified transmission modulationsignal.

[0091] Furthermore, the nonlinear distortion compensating section 600 isachievable by a surplus calculation performance of DSP (notillustrated), which is a component of the transmission apparatus. Thatis, calculation equations which are used by each power calculatingsection 602, compensation coefficient calculating section 604, anddistortion compensating section 606 is incorporated in programs of theDSP, and a coefficient which the compensation coefficient calculatingsection 604 uses for calculation is achievable by being stored in a dataarea in the programs of the DSP.

[0092] A description is given of the actions of the transmissionapparatus thus constructed. Firstly, an amplitude value 603 of atransmission signal is calculated by the power calculating section 602on the basis of the transmission digital quadrature base band signal601. This is calculated as shown in the following equation (1) where theamplitude value 603 is assumed to be “P”.

P=I ² +Q ²  (1)

[0093] Next, using the calculated transmission signal amplitude value603 as an input value, nonlinear distortion compensation data 605,having an inversed characteristic of the transmission system nonlineardistortion characteristics, in which the nonlinear distortioncompensation data is quadratured, is calculated by the compensationcoefficient calculation section 604. This is, for example, ann-dimensional polynomial in which P is used as an input, wherein thesame phase component Ci and quadrature component Cq are calculated as inthe following equations (2) and (3).

Ci=a _(in) P ^(n) +a _(in−1) P ^(n−1) + . . . +a _(i1) P ¹ +a _(i0) P⁰  (2)

Cq=a _(qn) P ^(n) +a _(qn−1) P ^(n−1) + . . . +a _(q1) P ¹ +a _(q0) P⁰  (3)

[0094] The distortion compensating section 606 provides a complexproduct of the transmission digital quadrature base band signal 601 andthe quadratured nonlinear distortion compensation data 605 and outputs aquadrature base band signal 607, the nonlinear distortion of which iscompensated. This is calculated as in the following equations (4) and(5) where I and Q channel components of the quadrature base band signal607 are respectively I′ and Q′;

I′=IC _(i) −QC _(q)  (4)

Q′=IC _(q) +QC _(i)  (5)

[0095] The quadrature base band signal 607 in which the nonlineardistortion is compensated is converted to analog signals by a D/Aconverting section 608, and is band-limited by a low band pass filter610, wherein an analog quadrature base band signal 611 is obtained.After quadrature modulation is carried out by a quadrature modulator 612and a modulated signal 613 is obtained, it is amplified to a necessarysize by a transmission system amplifier 614, wherein a transmissionmodulation signal 615 is outputted.

[0096] Furthermore, a quadrature modulator 612 is replaced for such atype as is able to carry out quadrature modulation of digital quadraturebase band signals, and a D/A converter and a low band pass filter may beconnected between the quadrature modulator and amplifier 614.

[0097] This, according to the sixth embodiment, the nonlinear distortioncompensating section 600 is constructed so that signal power is obtainedfrom the inputted quadrature base band signal, a distortion compensationcoefficient is calculated by an approximation equation for distortioncompensation, in which the value is used as a parameter, nonlineardistortion compensation is carried out using the distortion compensationcoefficient, and simultaneously the coefficient of the approximationequation is renewed using an error between the quadrature signalobtained by demodulating the output to which the modulation output isshared, and the quadrature base band signal. Therefore, nonlineardistortion compensating section 600 for compensating nonlineardistortions generated in the transmission system amplifier 614 can beconstructed to be small-sized without use of memory tables achieved by aRAM or a ROM, etc.

[0098] (Embodiment 7)

[0099]FIG. 7 is a main block diagram of a transmission apparatus of aseventh embodiment of the invention. However, parts of the seventhembodiment, shown in FIG. 7, which correspond to those of the sixthembodiment shown in FIG. 6 are given the same reference numbers, and thedescription thereof is omitted.

[0100] In FIG. 7, reference number 700 indicate a nonlinear distortioncompensating section, reference number 704 indicate a compensationcoefficient calculating section for amplitude distortion compensation,reference number 705 indicate amplitude distortion compensation data,reference number 707 indicate an analog quadrature base band signal,reference number 709 indicate a band-limited analog quadrature base bandsignal, reference number 711 indicate a modulation signal, referencenumber 712 indicate a gain controlling amplifier for amplitudedistortion compensation, and reference number 613 indicate a modulationsignal, the amplitude distortion of which is compensated. Furthermore,the nonlinear distortion compensating section 700 is achievable bysurplus calculation performance of the DSP (not illustrated), which is acomponent of the transmission apparatus.

[0101] A description is given of the actions of the transmissionapparatus thus constructed. First, amplitude value 603 of transmissionsignal is calculated by the power calculating section 602 on the basisof transmission digital quadrature base band signal 601. Next, theamplitude value 603 of the calculated transmission signal is used as aninput value, wherein amplitude distortion compensation data 705 havingan inversed characteristic of the amplitude distortion characteristic ofthe transmission system is calculated by the compensation coefficientcalculating section 704 using an approximation equation.

[0102] On the other hand, transmission digital quadrature base bandsignal 601 is converted to analog signals by D/A conversion section 608,and the band is limited by a low band pass filter 610, wherein an analogquadrature base band signal 709 is obtained. After quadrature modulationis carried out by a quadrature modulator 612 to obtain a modulationsignal 711, amplitude distortion compensation is carried out by a gaincontrolling amplifier 712 for compensating the amplitude distortion onthe basis of amplitude distortion compensation data 705, thereby causinga modulation signal 613 to be obtained, the amplitude distortion ofwhich is compensated. Finally, the signal is amplified to a sizenecessary for the amplifier 614, and a transmission modulation signal615 is outputted.

[0103] Furthermore, it may be constructed that the quadrature modulator612 is replaced for such a type that modulates the digital quadraturebase band signals for quadrature, and a D/A converting section and a lowband pass filter are connected between the quadrature modulator and gaincontrolling amplifier 712.

[0104] Thus, according to the seventh embodiment, since the nonlineardistortion compensating section 700 is constructed so that signal poweris obtained from the quadrature base band signal inputted, the amplitudedistortion compensation coefficient is calculated by an approximationequation for compensating the distortion, in which the value is used asa parameter, the amplitude distortion of the quadrature modulationsignal is compensated on the basis of the amplitude distortioncompensating coefficient using the same coefficient, and a modulationsignal is obtained, the amplitude distortion of which is compensated.Thus, the nonlinear distortion compensating section 700 can beconstructed to be small-sized without use of a memory table which isachieved by a RAM or ROM, etc.

[0105] (Embodiment 8)

[0106]FIG. 8 is a main block diagram of a transmission apparatusaccording to an eighth embodiment of the invention. However, parts ofthe eighth embodiment, shown in FIG. 8, which correspond to those of thesixth and seventh embodiments shown in FIG. 6 and FIG. 7 are given thesame reference numbers, and the description thereof is omitted.

[0107] In FIG. 8, reference number 800 indicate a nonlinear distortioncompensating section, reference number 816 indicate a directivitycoupler, reference number 817 indicate a transmission modulation signalshared, reference number 818 indicate a quadrature demodulator,reference number 819 indicate a quadrature base band signal, thequadrature of which is detected, reference number 820 indicate a lowband pass filter for limiting the band, reference number 821 indicate aquadrature base band signal, the band of which is limited, referencenumber 822 indicate an A/D converter section, reference number 823indicate digital quadrature base band signal, reference number 824indicate a coefficient renewing section. Reference number 825 indicatecoefficient data of an approximation equation for calculation of acompensation coefficient.

[0108] Furthermore, the power calculating section 602, compensationcoefficient calculating section 704 and coefficient renewing section 824of the nonlinear distortion compensating section 800 are achievablethrough the surplus calculation performance of the DSP (notillustrated), which is a component of the transmission apparatus.

[0109] A description is given of the actions of the transmissionapparatus thus constructed. Firstly, the amplitude value 603 oftransmission signal is calculated by the power calculating section 602on the basis of transmission digital quadrature base band signal 601.Next, the calculated amplitude value 603 of the transmission signal isused as an input value, wherein amplitude distortion compensation data705 having an inversed characteristic of the amplitude distortioncharacteristics of transmission system is calculated by the compensationcoefficient calculating section 704 using an approximation equation.

[0110] On the other hand, the transmission digital quadrature base bandsignal 601 is converted to analog signals by the D/A converting section606, and the band is limited by a low band pass filter 610, therebycausing an analog quadrature base band signal 709 to be obtained. Afterquadrature modulation is carried out by quadrature modulator 612 toobtain modulation signals 711, the amplitude distortion compensation iscarried out by a gain controlling amplifier 712 for compensating theamplitude distortion on the basis of the amplitude distortioncompensation data 705, thereby causing modulation signals 713 to beobtained, the amplitude distortion of which is compensated. The signalsare amplified to a necessary size by an amplifier 614, and transmissionmodulation signals 615 are outputted. At this time, the transmissionmodulation signals 615 are shared by a directivity coupler 816.

[0111] The shared transmission modulation signals 817 are detected by aquadrature demodulator 818. After they pass through a low band passfilter 820 for limiting the band, they are converted to digital signalsby an A/D converting section 822, thereby causing digital quadraturebase band signals 823 to be obtained. The coefficient data 825 of theapproximation equation is renewed by the coefficient renewing section824 so that the difference between the amplitude of digital quadraturebase band signal 823 and the amplitude value 603 of the transmissionsignal is minimized.

[0112] Thus, according to the eighth embodiment, the nonlineardistortion compensating section 800 is constructed so that signal poweris obtained on the basis of the inputted quadrature base band signals,the amplitude distortion compensation coefficient is calculated by anapproximation equation for compensating the distortion, in which thevalue of signal power is used as a parameter, an amplitude distortion ofthe quadrature modulation signal is compensated on the basis of theamplitude distortion compensation coefficient using the coefficient, themodulation signals, the amplitude distortion of which is compensated, isshared, and the amplitude compensation coefficient is renewed so thatthe difference between the detected signal (output signal) and the inputsignal having power obtained beforehand is minimized after the sharedmodulation signals are detected for quadrature. Therefore, the nonlineardistortion compensating section 800 can be constructed to be small-sizedwithout use of a memory table achievable by a RAM or ROM, etc., and atthe same time it is possible to compensate distortion changes due toenvironmental changes such as in temperature, etc.

[0113] (Embodiment 9)

[0114]FIG. 9 is a main block diagram of the transmission apparatus of aninth embodiment of the invention. However, parts of the ninthembodiment shown in FIG. 9, which correspond to those of the sixth andeighth embodiments shown FIG. 6 and FIG. 8 are given the same referencenumbers, and the description thereof is omitted.

[0115] In FIG. 9, reference number 900 indicate a nonlinear distortioncompensating section, reference number 904 indicate a fixed coefficientreference section by ROM, which refers to a fixed compensationcoefficient for compensating nonlinear distortions using the amplitudevalue 603, reference number 905 indicate a quadratured fixed nonlineardistortion compensation coefficient, reference number 908 indicate adistortion compensating section, reference number 926 indicate acoefficient renewing section, and reference number 927 indicatecoefficient data of an approximation equation for calculation ofcompensation coefficients.

[0116] Furthermore, the power calculating section 602, compensationcoefficient calculating section 604 and coefficient renewing section 926of the nonlinear distortion compensating section 900 are achievable bysurplus calculation performance of the DSP (not illustrated), which is acomponent of the transmission section.

[0117] A description is given of the actions of a transmission sectionthus constructed. First, the amplitude value 603 of transmission signalsis calculated by the power calculating section 602 on the basis of thetransmission digital quadrature base band signal 601 as in theabovementioned equation (1). Next, with reference to the fixedcoefficient reference section 904 as using the amplitude value 603 ofthe calculated transmission signal as an address, the nonlineardistortion compensation data having an inversed characteristic of thenonlinear distortion characteristics of the transmission systemcalculated in advance is obtained as a quadratured nonlinear distortioncompensation coefficient 905.

[0118] Herein, it is assumed that wherein the amplitude value 603 is Pas shown in the equation (1), a nonlinear distortion compensationcoefficient 905 corresponding to P is (di, dq).

[0119] Simultaneously, the amplitude value 603 of the transmissionsignal calculated is used as an input value, wherein a correctingcoefficient 605 for correcting the nonlinear distortion compensationcoefficient 905 is -calculated by the correcting coefficient calculatingsection 604 using the abovementioned approximation equations (2) and(3).

[0120] The distortion compensating section 908 carries out a complexproduct of a transmission digital quadrature base band signal 601, aquadratured nonlinear distortion compensation data 905 and correctingcoefficient 605, and outputs a quadrature base band signal 607, thenonlinear distortion of which is compensated.

[0121] This is calculated by the following equations (6) and (7), firstusing (di, dq) of the nonlinear distortion compensation coefficientwhere the I and Q channel components of the quadrature base band signal607 are respectively I″ and Q″.

I′=Idi−Qdq  (6)

Q′=Idq+Qdi  (7)

[0122] Next, (Ci, Cq) of the correcting coefficient 605 is used withrespect to the result of the abovementioned equations (6) and (7), andcalculation is made as in the following equations (8) and (9).

I″=I′Ci−Q′Cq  (8)

Q″=I′Cq+Q′Ci  (9)

[0123] The quadrature base band signals 607 for which the nonlineardistortion is thus compensated are converted to analog signals by a D/Aconversion section 608 and the band thereof is limited by a low bandpass filter 610, thereby causing analog quadrature base band signals 611to be obtained. After the signals are quadrature-modulated by aquadrature modulator 612 to obtain modulation signals 613, they areamplified by an amplifier 614 of the transmission system to a necessarysize, and transmission modulation signals 615 are outputted. At thistime, the transmission modulation signals 615 are shared by adirectivity coupler 816.

[0124] The shared transmission modulation signals 817 are detected by aquadrature demodulator 818, and pass through a low band pass filter 820for limiting the band. Thereafter, the signals are converted to digitalsignals by an A/D converting section 822 to obtain digital quadraturebase band signals 823. The coefficient data 927 of approximationequations for calculating the correcting coefficients are renewed by acoefficient renewing section 926 so that the difference between thequadrature base band signals 601 and 823 is minimized.

[0125] Thus, according to the ninth embodiment, the nonlinear distortioncompensating section 900 is constructed so that signal power is obtainedfrom the quadrature base band signals inputted, nonlinear distortioncompensation coefficients are obtained using the value of signal poweras a parameter, compensation coefficients are calculated byapproximation equations for compensating distortions to carry outdistortion compensations using the coefficients, modulation signals inwhich the distortion compensation signals are modulated for quadratureare shared, and the compensation coefficients of approximation equationsare renewed so that the difference between the detection signals (outputsignals) and input signals for which power is obtained in advance isminimized after the shared modulation signals are detected forquadrature. Therefore, the nonlinear distortion compensating section 900can be constructed so as to achieve high accuracy and compensate thedistortions changing in line with changes of the environments due totemperature changes, etc.

[0126] Furthermore, the respective nonlinear distortion compensatingsections 600, 700, 800, and 900 described above according to embodiments6 through 9 shown in FIGS. 6 through 9 may be replaced for any one ofthe nonlinear distortion compensating sections 104, 201, 501 shown inFIGS. 1 through 5. However, when replacing nonlinear distortioncompensation sections, it is necessary that a matching is secured withrespect to the type of quadrature modulators, positions of the D/Aconverting section and low band pass filter, and position of gaincontrolling amplifier 712 on the basis of the description made withrespect to the first through the ninth embodiments.

[0127] Furthermore, each of the nonlinear distortion compensatingsections 600, 900 may be composed of integrated circuits by a hardwareconfiguration using logic circuits, etc. individually, or with itstransmission apparatus included in a DSP (not illustrated), which is acomponent.

[0128] Still furthermore, three elements, that is, amplitude calculatingsection 101, limiting coefficient calculating section 301 and amplitudelimiting section 103 shown in FIG. 3 and FIG. 4 may be composed ofintegrated circuits by a hardware configuration combination with any oneof the respective nonlinear distortion compensating sections 600, 900,or they may be composed of integrated circuits by a hardwareconfiguration combined with any one of the respective nonlineardistortion compensating sections 600, 900, and included in the DSP.

[0129] In a case where they are composed of integrated circuits, thenonlinear distortion compensation can be carried out at a high speed.

INDUSTRIAL APPLICABILITY

[0130] As described above, a transmission apparatus according to theinvention is very useful as a transmission apparatus of radiocommunication systems and is suitable for compensation of nonlineardistortions generated in the transmission system.

What is claimed:
 1. A digital wireless communication system comprising:an amplitude limiting section that limits an amplitude of a sequence ofsignals input for transmission; and a nonlinear distortion compensatingsection that compensates nonlinear distortion of the sequence of signalsoutput from said amplitude limiting section.
 2. A digital wirelesscommunication system according to claim 1, wherein the compensatedsequence of signals output from said nonlinear distortion compensatingsection is converted to radio frequency signals and amplified fortransmission.
 3. A method for digital wireless communication comprising:limiting an amplitude of a sequence of signals input for transmission;and compensating nonlinear distortion of the amplitude limited sequenceof signals.